Multi-carrier modulation (MCM) techniques enable transmissions of a set of data over multiple narrow band sub-carriers. With an advanced wideband modulation and coding scheme, an MCM system may achieve higher spectral efficiency in frequency selective channels compared to systems using single carrier modulation techniques.
Orthogonal frequency division multiplexing (OFDM) is an example of a MCM technique used in a wireless communication system. OFDM divides the total bandwidth into several orthogonal sub-bands overlapping in frequency and may be efficiently implemented by fast Fourier transform (FFT). In practical wireless communication systems, cyclic prefix orthogonal frequency division multiplexing (CP-OFDM), (i.e., OFDM with CP), is used to combat multipath channel. With a long enough cyclic prefix (CP), a simple one-tap frequency domain equalizer (FDE) is sufficient to mitigate the multipath channel impairment. However, large sidelobes of the rectangular pulse in OFDM create challenging issues in practice, including large inter-carrier interference when the system is not perfectly synchronized and excessive out-of-band emission (OOBE) exists, which limits the effectiveness of OFDM in networks with dynamic channel access capabilities.